How much potting soil for a 12 inch pot?
A 12 inch pot holds about 11 dry quarts of potting mix (3.3 gallons) when it tapers to 9 in at the base, stands 10 in tall and is filled an inch below the rim. With 10% for settling, buy 12 dry quarts (0.48 cubic feet), so 1 bag of 16 qt is enough.
How to work it out
- Fill height 9 in; width at the fill line 11.7 in, bottom 9 in
- 3.1416 × 9 in ÷ 12 × (11.7² + 11.7 × 9 + 9²) = 3.3 gal per pot
- + 10% for settling = 0.48 cu ft (12 dry quarts) → 1 bag
"12 inch" describes the width across the top of the pot, not its volume, and pots of that width range from shallow bowls to tall cylinders. This example is an ordinary tapered pot of the kind sold for herbs, annuals and patio tomatoes. Measure across the inside of the rim; the lip can add half an inch that holds no soil.
Adjust for your project
More options: Settling · Bag price
- In dry quarts (as on the bag)
- 12 dry quarts
- Bags of that size
- 1 bag · 16 qt bag
- Each container holds
- 3.3 gal (12.5 L)
- Use potting mix, not garden soil or topsoil — soil packs down in a container and drains poorly.
Potting mix for a 12 in pot (9 in base), by pot height
| Pot height | Each container holds | In dry quarts (as on the bag) | Bags of that size |
|---|---|---|---|
| 8 in | 2.54 gal | 10 dry quarts | 1 bag |
| 10 in | 3.3 gal | 12 dry quarts | 1 bag |
| 12 in | 4.05 gal | 15 dry quarts | 1 bag |
| 14 in | 4.8 gal | 18 dry quarts | 2 bags |
What to know about filling a 12 inch pot
Shape changes the answer more than you would expect. A straight-sided 12 in pot of the same height holds closer to 15 quarts, and a tapered 12 in pot 12 in deep takes about 14, so the common range for this width runs from about 9 to 15 quarts.
A 16 qt bag fills one pot with a few quarts to spare, and an 8 qt bag falls short. For two of these pots, one 1 cu ft bag (about 25.7 dry quarts) covers both; four take two of those bags.
Think about what is going in it. At a little over 3 gallons, this pot is fine for herbs, flowers and a cherry tomato, which University of Maryland Extension says needs at least 2 gallons of mix. It is below the 5 gallon minimum they give for standard tomatoes, peppers, cucumbers and eggplant; for those, see How much potting soil for a 5 gallon bucket or grow bag.
Check for a drainage hole before you fill. Many glazed and decorative 12 in pots have none, and a pot without drainage stays waterlogged no matter how good the mix is. For the other end of the size range, see How much soil for a half whiskey barrel planter.
Different size? Use the full Potting Soil Calculator.
What you’ll need
- Potting soil scoopBudget price
Fills pots from a bag with less mess than a trowel.
See options on Amazon (opens in a new tab) - Rolling plant caddyBudget price
A wheeled base for big planters — set it down before you fill the pot.
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Frequently asked questions
How much potting soil for a straight-sided 12 inch pot?
About 15 dry quarts (4.41 gallons) at 10 inches tall, filled an inch below the rim; 17 dry quarts with 10% for settling.
How much potting mix for four 12 inch pots?
For four tapered pots 12 inches tall: 61 dry quarts (2.38 cubic feet) with 10% for settling, or 3 bags of 1 cu ft.
Other common sizes
- How much potting soil for a 5 gallon bucket or grow bag — 0.74 cu ft
- How much soil for a half whiskey barrel planter — 4.57 cu ft
Sources
- University of Maryland Extension: Growing Vegetables in Containers and Salad Tables (opens in a new tab) — Garden soil (~75 lb/cu ft) is too dense for containers; soilless mixes are ~10 lb/cu ft; minimum container sizes (5 gal for standard tomatoes, peppers, cucumbers, eggplant; 2 gal for cherry tomatoes).
- University of Maryland Extension: Types of Containers for Growing Vegetables (opens in a new tab) — All containers need drainage holes; half whiskey barrels and 5-gallon buckets as containers; growing-media volume and depth by plant size.
- NIST Handbook 44, Appendix C: General Tables of Units of Measurement (opens in a new tab) — 1 dry quart = 67.2006 cubic inches; 1 cubic foot = 1,728 cubic inches.